Measurements of D and H in the Upper Atmosphere of Mars with the MAVEN IUVS Echelle Channel

The enhanced ratio of D/H in the martian atmosphere has long been interpreted to provide evidence for the historic loss rate of water into space, with the enhancement resulting from the mass ratio of the species. Understanding the dependence of the enrichment of D on the loss rate of water requires that one understand the controlling factors, including all sources of exospheric hydrogen and the present-day transport of D and H into the upper atmosphere. Toward this end the MAVEN mission has included an echelle channel in the IUVS instrument that resolves the D and H Lyman alpha emissions produced by resonant scattering of bright solar emission. In this mode it has now been possible to measure the upper atmospheric D and H abundances over most of a martian year. The results are surprising, with larger than expected changes in the D and H abundances and a changing ratio of D/H with a strong seasonal dependence. This talk will present the D and H data to date (Mars will be near perihelion by the time of the DPS meeting) and discuss the interpretation of the large changes that have been observed.